Methods for scanning an examination subject by way of a CT system are generally known. For example, typical methods employed in such cases are circular scans, sequential orbital scans with patient feed-through, or spiral scans. Other types of scan that are not based on circular movements are also possible, such as e.g. scans with linear segments. Absorption data of the examination subject is recorded from different recording angles with the aid of at least one X-ray source and at least one oppositely located detector, and said thus collected absorption data or, as the case may be, projections are computed by means of appropriate reconstruction methods into sectional images (slices) through the examination subject.
In order to reconstruct computed tomographic images from X-ray CT data sets of a computed tomography device (CT scanner), i.e. from the acquired projections, a technique referred to as filtered back-projection (FBP) is currently employed as the standard method. Following the data acquisition a so-called “rebinning” step is performed in which the data generated by means of the beam spreading out from the source in the shape of a fan is reordered in such a way that it is available in a form as though the detector had been impinged upon by X-ray beams converging in parallel onto the detector. The data is then transformed into the frequency domain. Filtering takes place in the frequency domain and subsequently the filtered data is back-transformed. A back-projection onto the individual volume elements or “voxels” within the volume of interest is then performed with the aid of the thus re-sorted and filtered data.
A limited range of measurement, the field of view, is present due to the extent of the detector. This means that at a certain projection angle, projection and/or measured data can be acquired only for those voxels of an examination subject which lie within the field of view. Often, however, the problem arises that the extent of the examination subject is such that not all parts of the examination subject are located within the field of view during the entire period of measured data acquisition. This results in measured data sets that are incomplete in respect of said parts of the examination subject and consequently leads to artifacts being produced during the image reconstruction.